1. Field of the Invention
The present invention relates to a lens barrel which accomplishes zooming and focusing by a single drive mechanism, and a camera provided with the lens barrel.
2. Description of the Related Art
Integrated zoom and focus drive mechanisms are known which move various lens units on a single zoom line including alternating zooming intervals and focusing intervals as a construction for reducing cost and achieving compactness of the zoom lens barrel. An example of such a construction is described below with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are examples of zoom charts of a two-section zoom lens barrel which accomplishes focusing by a single lens unit (first section). This zoom lens barrel includes xe2x80x9ca stationary barrel which does not move relative to the camera bodyxe2x80x9d, xe2x80x9ca cam barrel which advances and retracts relative to the stationary barrelxe2x80x9d, and xe2x80x9cfirst and second lens units which advance and retract relative to the cam barrelxe2x80x9d identically to an embodiment of the present invention which is described later.
In FIG. 1A, straight line 1 presents the extension lead of the cam barrel relative to the stationary barrel, straight line 3 represents the relative extension lead of the first lens unit (first section) with regard to the cam barrel, and step line 2 represents the relative extension lead of the second lens unit (second section) with regard to the cam barrel. Accordingly, the amount of extension of the first lens unit relative to the stationary barrel is the combination of the straight lines 1 and 3, and is represented by the straight line 13 in FIG. 1B. Similarly, the amount of extension of the second lens unit relative to the stationary barrel is the combination of the straight line 1 and the step line 2, and is represented by the step line 12 in FIG. 1B.
This zoom lens barrel utilizes four middle steps M1, M2, M3 and M4 between telephoto end (tele) and wide angle end (wide), i.e., accomplishes zooming in a total of six steps, so as to accomplish focusing (focusing section F) using the part corresponding to the flat portions of the step line 12, and accomplish zooming (zooming section) using the other parts. In this way in an integrated zoom and focus drive mechanism, each lens unit moves on a single zoom line including alternating plurality of zoom sections and plurality of focus sections.
The curve 2xe2x80x2 in FIG. 1A represents the extension lead of the second lens unit (second section) relative to the cam barrel in the case of continuous zooming. Accordingly, the amount of extension of the second lens unit relative to the stationary barrel is represented by the curve 12xe2x80x2 in FIG. 1B. During continuous zooming, focusing at each zoom position is accomplished by changing the relative distance of both lens units using another drive mechanism.
As shown in FIG. 1B, the first section normally moves linearly along the zoom line 13 across all zoom regions, and the second section does not move in the optical axis direction in the horizontal parts (focusing section F) of the step-like zoom line 12. That is, the xe2x80x9crate of change of the relative distance between the first lens unit and the second lens unitxe2x80x9d with regard to a rotation amount (rotation angle) is the same in all focusing sections.
In general, it can be said that, in the zoom lens barrel, there is a large amount of movement of the focus position from the wide side to the tele side even when the change in the relative distance between the first section and the second section is the same. Accordingly, in a conventional integrated drive type zoom and focus zoom lens barrel wherein the rate of change of the relative distance between the first section and second section with regard to a barrel rotation angle (a constant rotation amount) is identical for all focusing sections, the amount of movement of the focus position increases relative to the same barrel rotation angle toward the tele side, as shown in FIGS. 1A and 1B, such that the focus precision disadvantageously decreases toward the tele side.
To eliminate this problem, consideration has been given to increasing the focusing resolution on the tele side as the total amount of rotation of the lens barrel increases, or increasing the amount of barrel rotation in the focusing section as the length of the zooming section becomes shorter. However, when the total amount of rotation of the barrel is increased, the total length of the cam channel (e.g., cam channel 210 shown in FIGS. 2xcx9c4) formed on the cam barrel also increases, and the strength of the barrel is reduced in that part, and the analogous cam channel overlap. Furthermore, when the number of zooming sections is reduced, the pressure angle increases in each zooming section, and as a result the smooth rotation of the barrel is hindered so as to produce another problem in that a large drive force is required for barrel rotation.
An object of the present invention is to provide a zoom mechanism using an integrated zoom and focus drive method which does not increase the total rotation of the barrel, does not increase the pressure angle in the zooming section, and does not adversely affect focus precision on the tele side.
The present invention attains these objects by providing a zoom camera having the characteristics describe below.
The zoom camera of the present invention has an integrated zoom and focus drive type zoom lens barrel which moves on a single zoom line and includes alternating plurality of focusing sections and plurality of zooming sections. With regard to the xe2x80x9cadjoining two lens units whose relative distance unit change most greatly affects the amount of movement of the focus positionxe2x80x9d, the xe2x80x9crate of change of the relative distance of the two lens units with regard to a barrel rotation anglexe2x80x9d in each focusing section becomes smaller in the focusing sections of the tele side.
In general, xe2x80x9cthe amount of movement of the focus position with regard to the change in the relative unit distance of the two opposing lens unitsxe2x80x9d increases from the wide side to the tele side. On the other hand, xe2x80x9cthe amount of movement of the focus position relative to a barrel rotation anglexe2x80x9d is expressed as the sum of xe2x80x9cthe amount of movement of the focus position (with regard to the change in the relative unit distance of the two opposing lens unitsxe2x80x9d and xe2x80x9cthe rate of change of the relative distance of the two lens units with regard to the barrel rotation angle.xe2x80x9d Accordingly, xe2x80x9cthe amount of movement of the focus position relative to the barrel rotation anglexe2x80x9d can be fixed in the entire zoom range by setting the rate of change of the relative distance of the two lens units with regard to the barrel rotation anglexe2x80x9d to be smaller in conjunction with the advance to the tele side. That is, the focus precision is not adversely affected with the advance to the tele side.
When there are only two lens units, the xe2x80x9crate of change of the relative distance of the two lens units with regard to the barrel rotation anglexe2x80x9d may be reduced in conjunction with the advance to the tele side in observation of these two lens units. When there are three or more lens units, similar setting is accomplished in observation of xe2x80x9cthe amount of unit change of the relative distance of the two opposing lens units to affect the greatest influence on the movement of the focus positionxe2x80x9d. Among the two opposing lens units, the two opposing lens units affecting the greatest influence on the movement of the focus position differs depending on the specific lens construction, but the present invention includes all such lens units.
According to the present invention, the two opposing lens units wherein the amount of unit change in their relative distance most greatly influences the movement of the focus position in the aforesaid zoom lens camera are constructed such that the rate of change of the relative distance of the two lens units with regard to a barrel rotation angle in each focusing section becomes smaller advancing to the tele side, and thereby provides a method whereby the amount of movement of the focus position is near constant relative to the throughout the entire zoom region.
The zoom camera of the present invention is constructed such that xe2x80x9cthe amount of movement of the focus position is near constant relative to the barrel rotation angle throughout the entire zoom regionxe2x80x9d and each lens unit moves on the zoom line. In this case the consideration is not given to the rate of change of the relative distance of only the two specific lens units among a plurality of lens units, but rather consideration is given to the change in relative distance between several groups of opposed lens units (desirably all groups).
In the present invention, xe2x80x9cthe amount of movement of the focus position relative to a barrel rotation angle is the amount obtained by dividing by the zoom lens F valuexe2x80x9d, but each lens unit moves on the zoom line such that the amount of such change remains constant throughout the entire zoom region. Since the focus width determined from the diameter of the allowable circle of confusion permitted at each focal length is proportional to the F value, consideration of the change not only in the amount of movement of the focus position but also in F value is advantageous from the perspectives of rotation angle and cam optimization. In this case also consideration is given to the change in relative distance between several groups (and desirably all groups) of lens units.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.